Toilets need a 3" minimum drain and I believe a 2" minimum vent (I am not a plumber). Cast iron is very heavy and from what I've heard is almost impossible to cut. I personnally would call in a plumber, to rough in the DWV system.

 

Cast iron is tough, need special tools to work it. Though one possible solution is to replace a section of it with PVC. Consider all the expense you might end up with, and see if splurging on a SaniFlo will be more economical.

 

Thanks for the replies. That saniflo is cool. Never knew anything like it existed. A bit pricey at $650+, but for tough applications, worth a look. I might would consider one for our existing basement.

 

It's pretty straight forward to cut in a three inch tee. Before you begin support the pipe on both sides of where you will be cutting (needs to be preminant not temporary support). Measure the tee that you just bought and cut out a section of the cast iron waste that size (make sure you get a straight cut). Use diamond sawzall blades, they're about ten bucks a blade and you may go through one or you may use three. It may take up to an hour of sawzalling if you have a really tough pipe or fifteen minutes if you're lucky.
Once you have the piece all cut out just install your tee using banded no hub clamps (not ferncos)

 

Marlin, makes a good point about supporting/bracing the cast iron before you cut into it.
To clarify the cut out & spliced process;You could also rent a caswt iron cutter, if there is room enough to operate near and around the pipe.
Regardless of how you cut it, you will also need to add a short section of PVC on either side of the PVC "T". These short sections will be the same outside diameter of the cast iron pipe, and long enough to accept 1/2 of the rubber clamped couplings on each end. So, allow for this overall measurement + about a half of an inch for lining it all up.:wink:

 

I should have asked the age of the case iron. I try to avoid using chain snap cutters on older pipe as they have a tendency to not cut straight or in some cases even crack right up the pipe. For something like this you need a pretty exact cut, if it cracks out too big a chunk you're going to be cutting further down the pipe and replacing with PVC.

The line that is currently cast iron will stay all cast iron, their is no reason to add PVC on either side. You want to get a 4"x3" no hub fitting, this is going to be a cast iron fitting. Cut a piece of your 4in line out the same length as that fitting (you could go just a tiny bit wider). You then use no hub clamps on either side of that to attach it to the cast you have now. A third no hub clap will transition the 3in cast to 3in PVC.

 

Thanks for all the info and insight. The cast iron is original I expect to the construction of the home, so circa 1960. The crawl space area under the house is about 30", so not alot of space to work with. In fact, by the time the pipe gets to where it elbows down into the ground, it is running on the ground and then slightly below grade.

I think this is a job best left to the professionals who will be liable for cracking the cast iron if that happens.

Thanks again for all the info!

 

The professionals will not be liable for the cast iron cracking. If it happens they will repair it and bill you for it. They won't hold themselves accountable for the sturdiness of 50 year old pipe.

 

Poor choice of words...By liable, I meant they'd be able to fix what they broke.